1. Technical Field
The disclosed embodiments relate to an exhaust gas control apparatus that performs urea water addition to exhaust gas and reduces and removes nitrogen oxide in the exhaust gas by selective catalytic reduction in which ammonia generated from urea water is used as a reducing agent.
2. Description of Related Art
In the exhaust gas control apparatus described above, a retro-suction control for suctioning the urea water back to a urea water tank from a pipe that sends the urea water to a urea adding valve is executed when an engine is stopped so that freezing of the urea water in the pipe is prevented, and a filling control for filling the pipe with the urea water is executed after the engine is started. The filling control is performed by a urea pump being driven so that the urea water is sent from the urea water tank to the urea adding valve by an amount which is enough for the pipe to be filled in a state where the urea adding valve is open. Nonetheless, when the engine is stopped within a short period of time after the engine is started and before any urea water addition to the exhaust gas has been executed, the filling control becomes in vain and thus the pump was driven unnecessarily. In the exhaust gas control apparatus according to the related art that is disclosed in Japanese Patent Application Publication No. 2010-101262, the filling control is performed after the engine is started and a catalyst bed temperature of a selective reduction-type catalyst device rises to close to an active catalyst temperature.